MICRO-LIGHT GUIDE SPECTROPHOTOMETRIC MEASUREMENT OF CHANGES IN LOCAL HEMOGLOBIN OXYGENATION AND CONCENTRATION IN THE RABBIT LUNG INDUCED BYHYPOXIA AND HYPEROXIA

Due to the high flexibility of the micro-light guides used with the Er langen micro-light guide spectrophotometer (EMPHO) the instrument can be coupled to the lung surface without interfering with the local lung mechanics. The local pressure exerted on the lung varies between 45 a nd 47 mg/cm(2). This enables the continuous investigation of local hae moglobin oxygenation and relative local haemoglobin concentration. The effect of different inspired oxygen concentrations on local oxygen sa turation of intravascular haemoglobin and relative local haemoglobin c oncentration was investigated in 6 rabbits. The animals were anaesthet ized, intubated and artificially ventilated. After thoracotomy, a ligh t guide was placed on the pleural lung surface and haemoglobin spectra were measured at a frequency of 5 Hz using the EMPHO. Two types of ch anges in the local haemoglobin concentration were observed; one was co rrelated with the respiratory cycle. During inspiration a decrease in relative local haemoglobin concentration was observed. Opposite change s occurred during expiration. These changes were observed with simulta neous changes in local haemoglobin oxygenation. The oxygenation increa sed during inspiration and decreased during expiration. The amplitude of the oxygenation changes depended on the fraction of inspired oxygen FiO2. A second type of reaction in local haemoglobin concentration wa s observed when the inspired oxygen concentration was decreased or inc reased by changing the FiO2. A decrease in the oxygen partial pressure in the inspired gas mixture (PiO2) was associated with an increase in relative local haemoglobin concentration, whereas an increase in PiO2 was accompanied by a decrease in relative local haemoglobin concentra tion. The hypoxic increase could be due to an increase in perfusion in the upper part of the lung induced by a hypoxic pulmonary hypertensio n.